The present invention relates to electrostatographic imaging and recording apparatus, and to assemblies in these apparatus for fixing toner to the substrates. The present invention relates particularly to fuser members, and fusing surface layers for fuser members, in the toner fixing assemblies.
Generally in electrostatographic reproduction, the original to be copied is rendered in the form of a latent electrostatic image on a photosensitive member. This latent image is made visible by the application of electrically charged toner.
The toner forming the image is transferred to a substrate, also referred to in the art as a “receiver”, such as paper or transparent film, and fixed or fused to the substrate. Where heat softenable toners, for example, thermoplastic polymeric binders, are employed, the usual method of fixing the toner to the substrate involves applying heat to the toner, once it is on the substrate surface, to soften it, and then allowing or causing the toner to cool. This application of heat in the fusing process is preferably at a temperature of about 90° C.-220° C.; pressure may be employed in conjunction with the heat.
A system or assembly for providing the requisite heat and pressure is generally provided as a fusing subsystem, and customarily includes a fuser member and a support member. The various members that comprise the fusing subsystem are considered to be fusing members; of these, the fuser member is the particular member that contacts the toner to be fused by the fusing subsystem. The heat energy employed in the fusing process generally is transmitted to toner on the substrate by the fuser member. Specifically, the fuser member is heated; to transfer heat energy to toner situated on a surface of the substrate, the fuser member contacts this toner, and correspondingly also can contact this surface of the substrate itself. The support member contacts an opposing surface of the substrate.
Accordingly, the substrate can be situated or positioned between the fuser and support members, so that these members can act together on the substrate to provide the requisite pressure in the fusing process. In cooperating, preferably the fuser and support members define a nip, or contact arc, through which the substrate passes. Also as a matter of preference, the fuser and support members are in the form of fuser and pressure rollers, respectively. Yet additionally as a matter of preference, one or both of the fuser and support members have a soft layer that increases the nip, to effect better transfer of heat to fuse the toner.
During the fusing process toner can be offset from the substrate to the fuser member. Toner transferred to the fuser member in turn may be passed on to other members in the electrostatographic apparatus, or to subsequent substrates subjected to fusing.
Toner on the fusing member therefore can interfere with the operation of the electrostatographic apparatus and with the quality of the ultimate product of the electrostatographic process. This offset toner is regarded as contamination of the fuser member. Therefore, improving the release of the fuser member fusing surface layer, and thereby preventing or at least minimizing this contamination, is a desirable objective.
Silicones, used for fuser member surfaces, are known to provide good release in toner fusing systems. However, the life of silicone fuser member surfaces is limited, because they suffer from wear due to abrasion by the receiver.
Further in this regard, release agents, such as silicone release fluids, can be applied to fuser members during the fusing process to combat toner offset. However, silicone fuser member surfaces may swell when used in conjunction with these agents. And this swell also is a factor that limits fuser member surface life, because it causes the surface to wear and degrade faster. Such wear may be reduced by increasing the silicone crosslink density; however, such increased crosslink density typically leads to brittle materials unsuitable for use as fuser member surfaces.
Reinforcing fillers, such as inorganic fillers, have been incorporated into fuser member fusing surface layers—both to reduce the indicated swell, and to provide desired material properties, such as resistance to wear, modulus and tear. Unfortunately, most inorganic fillers are characterized by high surface energy; because of this property they serve as sites for toner to adhere to, and thereby contaminate the fuser member surface. Polyester toners in particular are especially prone to interacting with high energy sites in this manner to cause such contamination.
Fluorosilicones and phenylsilicones have also been used to reduce swell caused by release agents. However, these materials suffer the same detrimental effects when reinforcing fillers are employed.
Low surface energy reinforcing fillers, such as polytetrafluoroethylene (PTFE) particulate fillers, have been employed. While these provide certain benefits, they are not always suitable. PTFE fillers have been found to have poor compatibility with silicones, and therefore their inclusion in silicone fusing surface layers has resulted in high wear rates.
It is accordingly an object of this invention to provide a fuser member fusing surface layer that not only exhibits good resistance against offset, against contamination—particularly by polyester toners—but also does not suffer excessive swell from release agents, especially silicone release agents. It is further an object of this invention to provide a fusing surface layer having good wear resistance. It is yet additionally an object of this invention to provide a fusing surface layer that does not require the presence of high energy reinforcing fillers.